Field of the Invention
One or more embodiments of the present invention relate to a positive active material for a lithium secondary battery, a method of preparing the same, and a lithium secondary battery including the positive active material.
Description of the Related Art
Representative rechargeable secondary batteries are lead-acid batteries, nickel hydrogen batteries, lithium secondary batteries, and the like. In particular, lithium secondary batteries have no memory effect in which they may lose energy capacity if charged when not fully discharged, have a high energy density per unit weight because Li is the lightest of all metals, have an electromotive force of 3.6 V, which is three times greater than that of nickel-based batteries, and are easily miniaturized. Due to these characteristics, lithium secondary batteries are widely used in mobile products, notebooks, electric tools, and the like, and are also expected to be used in hybrid electric vehicles (HEVs) in the future.
A lithium secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. When the lithium secondary battery is charged, lithium ions are deintercalated from the positive electrode and then move to the negative electrode. On the other hand, when the lithium secondary battery is discharged, lithium ions are deintercalated from the negative electrode and return to the positive electrode, in this regard, the electrodes or the electrolyte do or does not undergo a chemical reaction.
Currently, a lithium cobalt oxide, i.e., LiCoO2 (hereinafter, referred to as “LCO”) is used most widely as a positive active material of a lithium secondary battery. However, due to local distribution and scarcity of cobalt resources, manufacturing costs increase and a stable supply of the cobalt resources is difficult. To address these problems, research into a material for replacing the cobalt material has been actively conducted. A nickel-based composite oxide, such as nickel-manganese-cobalt (NMC), is a candidate material that overcomes the limitations, such as costs, stability, capacity, and the like, of materials, such as LCO, LNO(LiNiO2), or LMO(Li2MnO3), and research into the candidate material has recently been conducted actively.
However, known nickel-based composite oxides have no satisfactory capacity and stability and thus there is still room for improvement.